I think that sooner or later fans of ebooks will see the emergece of ebooks that are published in electronic formats only. At this point I have not seen nor have I heard of any books being puclished in electronic format only. When do you think a significant number of books published in one year will be published in electronic formats only?

Anyone small, big or otherwise. Like you I assume there has been a few at amazon that have published in electronic format only however I have not heard of nor have I seen anyone to publish electronically only.

Gee I did not know that and from such a well known author as well. Would you say that a significant number of books published have been in electronic only? Since only one major author has ventured into this area I would not say that the number of authors is significant as yet.

Yeah, I think Stephen King did that as a fun experiment when the tech was relatively new (and he is so prolific that he can afford to throw one in the wind and see what happens....). I doubt that many established authors have done this or would do this in the future. But for new authors, obviously there is a lower barrier to entry with publishing ebooks, than there is for printed books. So there are LOTS. Tons. Just look in the Deals and Freebies forum. And also the Authors Self Promotion forum. The question then becomes, how to distinguish your ebooks from the pack, and build up buzz and make it successful? Amanda Hocking and a handful of others (oh yeah, 50 Shades of Gray!!!) have been able to do it.

As for big-name authors (besides Stephen King) publishing ebook-only titles, I am not sure why they would want to do that?

It is already pretty well established in the romance genre to an extent. Digital First publishes electronically and then chooses successful novels for print runs. Harlequin did it a long time ago with Carina Press, which by the way is DRM free and very reasonably priced. Harper Collins has the Avon Impulse. The others of the Big Six, either have a digital first program established or they have announced plans for one.

I'm not a big Science Fiction reader but I believe they also have programs such as this.

BAEN has quite a few digital-only titles.
They also did an ebook format magazine.
They regularly do a form of Digital-first, eARCs (electronic Advanced Reader Copies) that lets readers buy a copy before it goes to printing.